In the field of information industry, a variety of image recording and printing methods have been developed and practically employed. Among them, ink-jet recording and thermal transfer recording (printing) are widely used because apparatuses for such recording methods are light-weight, downsized and noiseless, as well as excellent in their workability and maintenance. Those apparatuses, moreover, can be easily modified to perform color recording. In addition to the above methods, color electrophotographic printers and copy machines, which can give full-color electrophotographic images of high resolution, have been recently developed and brought on market.
In the ink-jet recording, there are three types of methods classified according to the kind of ink employed in printing process, namely, method with aqueous ink, oily ink or wax ink. In any of those methods, an image is formed by applying the ink in the form of fine droplets onto a recording sheet.
Methods of thermal transfer recording can be classified into two types. One is a method using a thermal transfer sheet having a support and a melting ink layer coated thereon. In this method, the thermal transfer sheet is imagewise heated from the support side to melt the ink, and then the imagewise melted ink is transferred onto a recording sheet to form an image. Another method uses a thermal transfer sheet comprising a sublimating dye and a resin of a high softening point. In this method, the thermal transfer sheet is imagewise heated to sublimate the dye, and then the imagewise sublimated dye is transferred onto a recording sheet.
An electrophotographic printing method generally comprises the steps of: imagewise exposing a light-sensitive material to light, to form a latent image; developing the latent image with a toner to form a toner image on the surface of the light-sensitive material; transferring the formed toner image onto a recording sheet; and fixing the transferred toner image under heating.
Images recorded by the above methods are sometimes required to have a high glossiness, as well as a high resolution. In more detail, an image printed on a recording sheet is desired to have a high glossiness which appears close to that produced by silver-salt photography. In order to give a high glossiness to the image, the image recording sheet generally needs to comprise a highly transparent image-receiving layer, which is often provided on a white film support.
A recording sheet of the above-mentioned type is shown, for example, in Japanese Patent Provisional Publication No. H5-51469. The publication discloses an image recording sheet comprising: a polyethylene terephthalate film support containing calcium carbonate; and an image-receiving layer containing acrylic polymer emulsion, poly(vinyl alcohol), and colloidal silica. The image-receiving layer of the recording sheet has a relatively high transparency, and is provided on the white polyethylene terephthalate support film. Besides this, other white film supports are also known. Examples of such films include a polyester film containing dispersed barium sulfate particles (Japanese Patent Publication No. 60-30930), a polyester film containing calcium carbonate in an amount of 8 to 30 weight % (Japanese Patent Publication No. H7-15012), and a polyester film containing titanium oxide (Japanese Patent Publication No. H7-149926).
The present inventors, however, have noted that the known image recording sheet often gives an image of poor quality, especially from the viewpoint of graininess. In more detail, the known recording sheet often gives an image of a low quality such as an image having a series of beads-like spots of ink or toner (i.e., beading).